1. Field of the Invention
The present invention relates to an antenna device preferably for use in an RFID system or a near field radio communication system, and a communication apparatus including the antenna device.
2. Description of the Related Art
In general, in a 13.56 MHz-band RFID system, such as NFC (Near Field Communication), implemented in a mobile terminal, an RFID IC chip and a matching element are mainly mounted on a circuit board, an antenna is attached to the inner side of a terminal casing made of a resin, and the antenna and a terminal on the circuit board are DC-connected to each other via a spring pin or the like.
Meanwhile, a radio communication apparatus such as a recent cellular phone terminal has been thinned. In order to deal with insufficiency of strength due to thinning, a resin casing is subjected to magnesium plating or a metal casing is used to “metalize” the casing to supplement strength of the cases. However, when the casing is “metalized”, an antenna included in the terminal is shielded by a metal, and thus a problem arises that communication with a counterpart apparatus is disenabled.
Therefore, an antenna device has been proposed which has a structure in which a metal plate having a larger area than that of an antenna coil is caused to be close to (magnetically coupled with) the antenna coil, and is used as a radiator, as in Japanese Unexamined Patent Application Publication No. 2011-97657.
However, in Japanese Unexamined Patent Application Publication No. 2011-97657, a slit is formed in the metal plate. Thus, in the case where the metal plate is a part of a casing of a radio communication apparatus, there is a problem in that limitations on design arise (appearance is impaired) due to exposure of the slit.